The peculiar pleurocerids of the Interior Highlands I: Pleurocera potosiensis

You all like maps, am I right?  Who among my elite and erudite readership does not, at least occasionally, revel in an old-time paper map, and lament their impending extinction?

 So last summer I was taking a walk down memory lane in Derring Hall, home to both the Biology Department and the Geology Department at my alma mater [1], Virginia Tech (1973 – 1977).  And I stopped to admire a gigantic (1996) Tectonic Map of North America [2], preserved behind floor-to-ceiling Plexiglas sheeting outside the Geology Department office.  And snapped the photo below.

I was stricken by the obvious inference that at some point in the ancient past, a chunk broke off my old familiar East Tennessee stomping grounds and floated west beyond the Mississippi into the wilds of Arkansas and Oklahoma.  That chunk is the Ouachita Mountains.  Indeed, the tectonic theory of North America suggests that the Ouachita Mountains and the Appalachians are “sisters,” created together by the collision of the Gondwanan plates around 300 mya, subsequently separated by the Cretaceous Embayment.

 

Like most of us here in The East, I tend to lump the Ouachita Mountains together in my mind with the Ozark Highlands, but the Ozarks were uplifted as a dome and subsequently dissected.  That rugged region, extending north from NW Arkansas well into Missouri, is not visible in the 1996 map above.  I cannot find any consensus on the date or cause of the Ozark uplift; it may also have been a function of the Paleozoic orogeny that formed Ouachita Mountains, or may have been post-Paleozoic.  That doesn’t matter for the yarn I’m fixin’ to spin.

 

Melania potosiensis [6]

The most important thing is the snails.  Today, the characteristic freshwater gastropod of the USGS Interior Highlands Physiographic Division, which includes the Ozark Highlands, the Ouachita Mountains, and the Arkansas Valley between them, is Pleurocera potosiensis.  That snail is a regional endemic – widespread and locally quite common in rivers and streams throughout the physiographic division, unknown elsewhere.  Shi-Kuei Wu and colleagues [3] documented populations across the entire southern half of Missouri, an observation we have now thoroughly confirmed [FWGMO map].  Christian and Hayes [4] reported P. potosensis populations equally widespread across the northwestern quarter of Arkansas.  The species range also extends westward into Oklahoma, and touches the SE corner of Kansas [FWGGP map].  Further south, populations of P. potosiensis become less common in tributaries of the Arkansas River, and spotty in tributaries of the Ouachita.

Isaac Lea’s brief, Latinate description of Melania potosiensis appeared in 1841 [5], as #46 in that same “litter of 57 pleurocerid puppies” I catalogued in my essay of [20Aug25], with a more complete English description and figure following in 1843 [6].  Tryon [7] transferred the nomen to Goniobasis, reprinting Lea’s 1843 description verbatim, while adding, perceptively, 

“Were it not for the wide differences of locality I should suspect this to be identical with simplex.  I have not seen specimens, but the figure and description are certainly very close to that species.”

Goodrich [8] recognized four subspecies.  The most widespread he identified as Goniobasis potosiensis plebius (Anthony 1850), which he considered common in rivers and creeks throughout the Ozarkian area of Missouri, Arkansas, and Eastern Oklahoma.  The typical subspecies Goniobasis potosiensis (ss) he considered “a shell of the upland streams of a few Missouri counties” only.  Goodrich also recognized a Goniobasis potosiensis crandalli (Pilsbry 1890) “known only from Mammoth Springs, Fulton County, Arkansas” and a Goniobasis potosiensis ozarkensis (Call 1886) which he considered a “depauperate” form [9, 10], “only from springs of Shannon, Carter, Washington, Dent, and Camden counties, Missouri.”  Burch [11] transmitted Goodrich’s entire four-subspecies system along with their ranges verbatim, pausing only to swap out the well-established genus Goniobasis for the zombie taxon [12] Elimia.

 

As a laboratory for the study of evolution, the widely-dispersed and genetically diverse Ozark/Ouachita populations of P. potosiensis may rival the Pleurocera proxima populations of the southern Appalachians [14].  By the Grace of God, they seem to have slipped through 200 years of malacological malpractice to arrive in the 21st century almost unsplit by taxonomic exuberance.  Our colleague Russ Minton and his coworkers took advantage of this happy situation in both a shell morphological study [15] published in 2011, and in a 2017 study of intraspecific genetic divergence [16].

 

The 2011 paper, a landmark-based study of 500 individual shells sampled at 25 m intervals from a spring run and adjacent tributary of the Ouachita River in Garland County, Arkansas, was most memorable for its peculiar Figure 1.  True to the school of landmark-based morphometrics, there was no scale on Minton’s photo, reproduced below.  The caption simply read, “Morphological variation in Elimia potosiensis from Arkansas.”

Minton et al. [15] Figure 1

The first thing that struck me when I read Minton's 2011 paper some years ago was that the second shell (B) was clearly that of Leptoxis arkansensis, not P. potosiensis at all.  I’m sure that’s a common mistake, to naïve eyes.  I myself had no field experience in The Interior Highlands until 2024.  All I knew about the malacofauna of that biogeographically fascinating part of the world until quite recently was what I had learned from a week studying the Wu-Oesch-Gordon Missouri collections at the University of Colorado Museum in 2021, and even there I found some not-insubstantial Leptoxis/Pleurocera confusion.

But what really struck me upon my first reading of Minton’s 2011 morphometric study was that third shell (C).  It was clearly out of scale with the other two – probably 30% magnified, by my eye.  And recalling the words of Tryon, I found that shell completely indistinguishable from my old friend from the East, Pleurocera simplex. 

 

I picked up my first Pleurocera simplex when I was a student at Virginia Tech back in 1975, and since then have sampled hundreds of populations from SW Virginia all across Tennessee, Kentucky, and north Alabama.  I have published five papers and notes on P. simplex thus far [17], supplemented by at least eight blog posts.  Rob Dillon knows Pleurocera simplex.  Were populations of P. simplex on that plate-tectonic raft when it broke loose from its Tennessee moorings and washed up on the banks of the Wide Missouri way back in the Paleozoic?

 

Russ Minton’s 2017 paper was an even more interesting read.  He and his colleagues reported the results of two separate studies, a fine-scale study using ISSR markers very similar to the allozyme study I published on P. proxima way back in 1988 [14], and a study of 16S sequence divergence at the scale of many of the allozyme studies I published on P. proxima and others in the early-2000s [18].  The fine-scale study was poorly designed, with only 10 snails sampled for each of 12 sites down approximately 500 meters of stream, such that the ISSR markers (110 unique genotypes among the 120 individuals) returned no results.  But the study of mtDNA sequence divergence was fascinating.

Adapted from Figure 1 of Minton et al [16]

Minton and colleagues sequenced the 16S gene from 61 individual snails identified as “Elimia potosiensis” from 16 sites in southern Missouri, 14 sites in northern Arkansas, and 1 site in eastern Oklahoma.  Their map of sample sites, color-coded by drainage system, is reproduced above. This is the second-best data set [19] on interpopulation mtDNA sequence divergence ever published for any nominal species of pleurocerid snail.

 

Minton discovered four strikingly different sets of sequences, each about 10% different from the other three, none of which demonstrated any correlation to geography whatsoever.  Minton’s Figure 4 is reproduced below.  I have labelled those four sets of haplotypes X, Y, Z, and L.

 

Who among my loyal readership finds this result surprising, in the least?  How many blog posts have I dedicated to the phenomenon of mitochondrial superheterogeneity in freshwater gastropods [20], since Bob Frankis and I first stumbled upon the phenomenon [21] back in 2004?  Speaking now to any new visitors we might be entertaining in the columns of the FWGNA Blog this month, and to any other readers who might otherwise imagine that double-digit mitochondrial sequence diversity is unusual within pleurocerid populations, you are earnestly invited to footnote [22] for approximately 30 minutes of remedial study. 

Adapted from
Minton [16] Fig. 4

Ah, but.  Some of the details in Minton’s Figure 4 did not match the expectation I have developed over years of familiarity with mtSH.  Yes, Minton identified a majority haplotype, which I have labelled X, just as Whelan and Strong found in the best study of mtSH to date, their 2016 paper on Alabama Leptoxis [19].  Whelan & Strong also discovered five other haplotypes, all demonstrating double-digit sequence divergence from the majority haplotype, four of which were quite rare.  My jetlagged wildebison model would suggest that those five rare Leptoxis haplotypes had evolved somewhere far away (in snail-space or snail-time) to be scattered into the present-day study area by dirty birds.  And in the case of the Whelan & Strong dataset, we cannot identify four of those other five places.  Fine.

And yes in fact, the cluster I have labelled Y in Minton’s Figure 4 does fit our expectation for mtSH, under the jetlagged wildebison model.  That haplotype is 10.1% different from haplotype X, it is rare, and there is no divergence among the five individuals (found in three populations) carrying it.

 

But the clusters labelled Z and L in Minton’s Figure 4 do not look like mitochondrial superheterogeneity to me.  They are not rare.  Moreover, both show evolutionary structure – a branching within cluster.  Within cluster Z, for example, Population #2 branches first – the only two individuals sampled for the study, together.  Then population OK (from Oklahoma) branches off – all three of the individuals sampled, together.

 

And as I sat at my desk late one evening several years ago, examining the population OK data published in that paper, a bell tinkled way in the back of my addled brain.

 

Russ Minton only figured one shell in his 2017 paper, pasted into the corner of his Figure 2, showing a map of the sample sites for his ISSR study.  Quoting his Figure 2 caption: “Shell of E. potosiensis from population OK is shown.”  I have clipped that shell from Russ’ 2017 Figure 2 and pasted it in the lower left corner of my adaptation of his Figure 1 map above.  That is very clearly the same scaleless individual shell he labelled “Elimia potosiensis from Arkansas” in his 2011 paper.  And that shell looked as much like Pleurocera simplex in 2017 as it did in 2011.

 

All three of the individual snails that Minton sequenced from Oklahoma carried haplotype Z.  And the other 13 individuals carrying haplotype Z were scattered all across Minton’s three-state study area, as I have marked in red above.  In what direction could all those clues be leading?  Tune in next time.

 

Notes:

 

[1] For sweet, gauzy memories from my halcyon days at dear old Virginia Tech, see:

• Water hardness, stream size, and A.E. Boycott: A New River Reminiscence. [8July25]

[2] Muehlberger, W.R. (1996) Tectonic Map of North America.  American Association of Petroleum Geologists, Tulsa, OK.

 

[3] Wu, S-K., Oesch, R. & Gordon, M. (1997) Missouri Aquatic Snails. Jefferson City: Missouri Department of Conservation. 97 pp.

 

[4] Christian, A. D. and D. M. Hayes (2007) Diversity and distribution of freshwater gastropods from the Ozark Region of Arkansas.  Arkansas Game & Fish Commission, unpublished report. 34 pp.

 

[5] Lea, Isaac (1841) Continuation of Mr. Lea's paper on New Fresh Water and Land Shells.  Proceedings of the American Philosophical Society 2: 11 – 15.

 

[6] Lea, Isaac (1843) Description of New Fresh Water and Land Shells.  Transactions of the American Philosophical Society (New Series) 8: 163 – 250.

 

[7] Tryon, G. W. (1873) Land and Freshwater shells of North America Part IV, Strepomatidae.  Smithsonian Miscellaneous Collections 253: 1 - 435.

 

[8] Goodrich, C. (1939) Pleuroceridae of the Mississippi River basin exclusive of the Ohio River system.  Occasional Papers of the Museum of Zoology, University of Michigan 406: 1 – 4.

 

[9] We first mentioned “depauperization” in our essay of [20Aug25] on Melania acutocarinata.  Goodrich [10] defined “depauperization” as “the outward manifestation of disease, accident or malnutrition or a reaction to inimical environment.”

 

[10] Goodrich, Calvin (1939) Aspects of depauperization.  The Nautilus 52: 124 – 128.

 

[11] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI).

 

[12] We reviewed the taxonomic controversy here:

• Goniobasis and Elimia [28Sept04]

It ultimately didn’t matter, because both Goniobasis and Elimia were synonymized under Pleurocera by Dillon [13] in 2011.

 

[13] Dillon, R. T., Jr. (2011) Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque, 1818). Malacologia 53: 265-277. [pdf]  For a review, see:

• Goodbye Goniobasis, Farewell Elimia [23Mar11]

[14] General references on the population genetics of P. proxima:

Dillon, R.T. and G.M. Davis (1980) The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships. Malacologia 20: 83-98. [pdf]

Dillon, R.T. (1984) Geographic distance, environmental difference, and divergence between isolated populations. Systematic Zoology 33:69-82. [pdf]

Dillon, R.T. (1988) Evolution from transplants between genetically distinct populations of freshwater snails. Genetica 76: 111-119. [pdf]

Dillon, R.T. (1988) The influence of minor human disturbance on biochemical variation in a population of freshwater snails. Biological Conservation 43: 137-144. [pdf] For a review, see:

• Intrapopulation gene flow: The polymorphic Pleurocera of Naked Creek [12Oct21]

[15] Minton R.L., Lewis E.M., Netherland B, Hayes D.M. (2011) Large differences over small distances: plasticity in the shells of Elimia potosiensis (Gastropoda: Pleuroceridae). International Journal of Biology 3(1): 23 - 32.

 

[16] Minton, R.L., B.L. McGregor, D.M. Hayes, C. Paight, and K. Inoue (2017) Genetic structuring in the pyramid Elimia, Elimia potosiensis (Gastropoda, Pleuroceridae), with implications for pleurocerid conservation. Zoosystematics and Evolution 93(2) 437-449.

 

[17] General references on the population genetics of P. simplex in the Southern Appalachians:

Dillon, R. T., Jr., & G. M. Davis (1980) The Goniobasis of southern Virginia and northwestern North Carolina: Genetic and shell morphometric relationships. Malacologia 20: 83-98. [pdf]

Dillon, R. T., Jr., & J. D. Robinson (2007) The Goniobasis ("Elimia") of southwest Virginia, I. Population genetic survey. Report to the Virginia Division of Game & Inland Fisheries, 25 pp. [pdf]

Dillon, R. T., Jr. (2016a) Two reproductively isolated populations cryptic under Pleurocera simplex (Say, 1825) inhabiting Pistol Creek in Maryville, Tennessee. Ellipsaria 18(2): 15-16. [pdf]

Dillon, R. T., Jr. & J. D. Robinson (2016) The identity of the "fat simplex" population inhabiting Pistol Creek in Maryville, Tennessee. Ellipsaria 18(2): 16-18. [pdf]

Dillon, R. T., Jr. (2016) Match of Pleurocera gabbiana (Lea, 1862) to populations cryptic under P. simplex (Say, 1825) Ellipsaria 18(3): 10 - 12. [pdf]

 

[18] Regional surveys of pleurocerid population genetics:

Dillon, R. T. and A. J. Reed (2002) A survey of genetic variation at allozyme loci among Goniobasis populations inhabiting Atlantic drainages of the Carolinas.  Malacologia 44: 23-31. [pdf]

Dillon, R T. and J. D. Robinson (2009) The snails the dinosaurs saw: Are the pleurocerid populations of the Older Appalachians a relict of the Paleozoic Era?  Journal of the North American Benthological Society 28: 1 - 11.  (Rosemary Mackay Award)  [pdf]

Dillon, R. T. and J. D. Robinson (2011) The opposite of speciation: Population genetics of Pleurocera (Gastropoda: Pleuroceridae) in central Georgia.  American Malacological Bulletin  29: 159-168.  [pdf]

 

[19] The blue ribbon goes to the data set of Whelan, N.V. & E. E. Strong (2016) Morphology, molecules and taxonomy: extreme incongruence in pleurocerids (Gastropoda, Cerithiodea, Pleuroceridae). Zoologica Scripta 45: 62 – 87.

 

[20] A search on the word “superheterogeneity” using the box in the upper right of your screen will return hits in an impressive 24 essays.  And that doesn’t even include the essays I posted on the subject before I coined the term “mitochondrial superheterogeneity” in 2016.

 

[21] Dillon, R. T., and R. C. Frankis. (2004) High levels of DNA sequence divergence in isolated populations of the freshwater snail, Goniobasis.  American Malacological Bulletin 19: 69 - 77. [pdf]

 

[22] Mitochondrial superheterogeneity (mtSH), where two or more of the members of a single population demonstrate greater than 10% divergence in any single-copy mtDNA gene, not sex linked, is remarkably common in freshwater gastropods.  In pulmonate populations, I wouldn’t be surprised if most or all mtSH is ultimately traceable to cytoplasmic male sterility [23].  In prosobranch populations, however, I think mtSH is a signature of great age, plus low-frequency long distance dispersal, the “Jetlagged Wildebison Model.”  Here is a sample of my previous posts on mtSH:

• The Snails the Dinosaurs Saw [16Mar09]
• Mitochondrial superheterogeneity: What we know [15Mar16]
• Mitochondrial superheterogeneity: What it means [6Apr16]
• Mitochondrial superheterogeneity and speciation [3May16]
• Mitochondrial heterogeneity in Marstonia lustrica [3Aug20]
• Testing the periwinkle hypothesis [9May23]

[23] David, Patrice, Cyril Degletagne, Nathanaëlle Saclier, Aurel Jennan, Philippe Jarne, Sandrine Plénet, Lara Konecny, Clémentine François, Laurent Guéguen, Noéline Garcia, Tristan Lefébure, Emilien Luquet (2022) Extreme mitochondrial DNA divergence underlies genetic conflict over sex determination.  Current Biology 32: 2325 - 2333.  https://doi.org/10.1016/j.cub.2022.04.014.  For a review, see:

• Cytoplasmic Male Sterility in Physa! [9June22]

Art, science, and public policy: A dialogue in three languages

I have a lot of friends and family who enjoy travel, and spend a substantial amount of time and money doing it, and imagine that their hobby returns some sort of profit to the intellect or character.  Isn’t travel broadening?  Don’t we learn from exposure to new lands, new cultures, new value systems, new ways of looking at the world?  Yes, of course.  But I found countless worldviews, cultures, and value systems trumpeted in the newspaper at the end of my driveway this morning, ripe for engagement in the aisles of the grocery store across the street this afternoon.  No further travel is required.

As my loyal readership will attest, I have long been fascinated by the diversity of worldviews I encounter in my workday life, and the relationships between them.  The index item at the right of your screen labeled “Worldview Collision” will link to eight essays on the subject when I push the “submit” button on the present post.

The majority of my seven previous essays have explored the relationship between the worldview of science and the worldview of law or public policy, among the most common of the culture clashes in my experience. To understand their proper relationship I have adapted an analogy I first developed about twenty years ago during the height of the most recent creation/evolution controversy between science and religious faith.  Scientists play baseball, lawmakers and regulatory agencies play banjo.  Those worldviews are not incompatible, in the sense that my father was both a banjo picker and a catcher on his high school baseball team.  But not compatible, either.  Nobody ever tries to integrate one with the other. 

I favor the baseball/banjo analogy because most of my colleagues in the world of science seem to have a better grasp on the proper relationship between sports and art than between science and anything else, possibly because we are more objective in the former situation.  We don’t write grant proposals to shortstops, nor debate fiddlers over the 10th grade biology curriculum.

 

Nor collaborate with artists [1].  Thus, an email I received this past August (18Aug25) from one Ms. Julia Galloway [2] fell upon my eye as dew drops from heaven.  She introduced herself as: 

“… a professor and ceramic artist based in Montana. I’m currently working on a project focused on raising awareness about endangered species. For this project, I am creating ceramic urns to represent each threatened, endangered, recovered, and extinct species in the U.S. The project will culminate in the creation of approximately 1,200 urns, with completion expected by 2027.”

Ms. Galloway went on to explain that she had created “400+” urns as of that mid-August date and had (apparently) worked down from the California Condors to the freshwater gastropods, finding her supple hands now poised over a throw of clay to be entitled, “Anthony’s Riversnail.”  And googling about the internet for inspiration, she had found my “fabulous photo” posted on the FWGNA site.  And requested permission to use.

 

How fascinating!  The concept of “endangerment” is purely a matter of law, of course, and “raising awareness” a political objective.  Here an artist addresses a scientist over a matter of public policy. A conjunction of three worlds.

 

On 21Aug25 I replied to Ms. Galloway certifying, as I always do, that all of the images on the FWGNA site are freely available for anybody to use for any purpose whatsoever, and offering to help her in any other way I could.  And I concluded, doing my best to address her in her native tongue: 

“Notice that there's a photo of Leptoxis crassa (“Anthony’s Riversnail”) in situ at the bottom of (the species) page [here].  Which brings me to my final point.  Bless your heart!  These things are brown bumps on a rock.  God made them by throwing little balls of clay at dirt.  If you can make art out of Leptoxis crassa, my cap's off to you.”

 And to the bottom of my email of 21Aug25 I added, “PS – 1,200 urns? Are you nuts?”

Brown bumps in Limestone Creek, AL.

Here the challenge of communication across cultures was on full display.  At no point in her initial email to me, nor indeed in any of her subsequent correspondence, did Ms. Galloway mention the rich symbolism just below the surface of her artwork.  Her urns are modeled after the funerary urns of ancient Egypt.  But, quoting from her website, “displayed empty as a sign of hope.”  Anthony’s Riversnail may be gasping for breath, by this metaphor, but it ain’t dead yet.

 

Ms. Galloway replied immediately thanking me for my “delightful and thoughtful reply,” confessed that she does feel a little bit nuts at times, and asked me if I would like to see images of the urn upon completion. And I responded immediately in the affirmative, and suggesting that she just “throw a couple balls of clay at a flowerpot” to expedite the process.

 

I was tremendously impressed to receive the set of three jpegs below on the afternoon of 22Aug25, less than 24 hours after I had granted Ms. Galloway permission to use FWGNA imagery.  Maybe I shouldn’t have been so surprised – with 400 urns down and 800 to go, she must be nothing if not efficient.  Three individual snails were depicted various faces of the Anthony’s Riversnail urn, one snail crawling to the left (a) and two crawling to the right (b, c), as from the vantage point of a wary stonefly.  None of these images was modeled, as far as I could tell, from anything on the FWGNA site.  At least overtly.

 

Although starkly beautiful in their execution, I immediately noticed a couple significant technical problems with the imagery.  Or at least, they seemed significant to me.  So on 23Aug25 I addressed my third email to Ms. Galloway.

And this time, I felt compelled to speak a little bit of science.  I began with some background on gastropod coiling, so as to introduce the adjectives “sinistral and dextral,” and noted that no case of sinistrality has ever been documented in the Pleuroceridae, as far as I know.  I then wrote:

“You have depicted three individual snails on your urn, am I correct?  The images of which you labeled on the jpegs you sent me yesterday afternoon AO22-a, AO22-b, and AO22-c, yes?  Snail (b) is bearing a dextral shell, correct as you have sculpted.  But snail (a) and snail (c) are bearing sinistral shells.  Not only is that uncomfortable to my eyes, it is unscientific.”

That seemed harsh.  So I added, to soften the blow:

“Perhaps you were working from (somebody else's) closeup photograph of a pleurocerid animal, reversed in some popular publication or on the internet?   Amateurs often publish reversed images, careless of the difference.  In fact, it seems highly unlikely to me that anybody other than a professional malacologist would ever notice the chirality of the snails you have sculpted on your urn.  So if you want to let it go (as Queen Elsa would suggest) I would certainly understand.”

Well, a couple weeks passed.  And I honestly did not think I would ever hear from Ms. Galloway again.  At the rate of one urn per 24 hours, I imagined that she must be well into the unionid mussels by that point, gastropods let go, gone, and forgotten.  But on 2Sept25, I was most pleased to receive yet another lovely communication from my artist-pen-pal:

“Thank you so much for bringing chirality to my attention! I loved reading your email and learning more about gastropods. It's always a treat when I get to hear someone talk passionately about their field of study (especially when they're brown bumps on a rock).

 

Sometimes species have very few images, which was the case with this species. Not knowing about chirality, I flipped some of the images to give myself more viewing angles and compositional options. Now that I know about how snail shells grow, I would like to remake the urn. Would you happen to have any additional images of Anthony's River Snail that you could share?

 

Thank you again for taking the time to share this information with me and for your support! Take care and I hope to hear from you again soon!”

Well no, I myself did not have any additional photos of L. crassa showing anything that the couple images already posted on the FWGNA species page did not.  But on a whim, I executed simple a google-image search on “Athearnia anthonyi” and landed, of course, on the Wikipedia page [3].  And good grief.  The image at the top of the Wikipedia page is sinistral!

Wikipedia. From Dick Biggins, USFWS.

So on the evening of 4Sept25 I addressed my fourth email message to Ms. Galloway, apologizing on behalf of the entire profession of freshwater malacology, re-assuring her that Dick Biggins (the donor of the photo) is a careful worker and confessing that I could not imagine that he himself would upload a mirror-reversed image.  But regardless of how the error occurred, I was sorry that some member of our extended community had not fixed it by now.  Not it.

 

I then suggested three remedies: (1) Sculpt the Wikipedia image from a mirror, (2) Adjust the Wikipedia image using the Photoshop mirror-image-reverse button, or (3) model from some other pleurocerid. Honestly, at the resolution of a funerary urn, all pleurocerid bodies are indistinguishable.  I sent her a good image of some other pleurocerid individual crawling to the viewer’s right, so that she would have both left-travelling dextral and right-travelling dextral models to work from.

 

And on 7Sept25 Ms. Galloway thanked me once again, and asked me if I would like to see images of “the new and improved urn when it is completed?”  To which I replied in the affirmative.  But I never heard from her again.  And that’s OK.

 

The philosopher Ian Barbour (1923 – 2013) has suggested [4] that there are four ways in which worldviews might relate: (1) independence, (2) dialogue, (3) conflict and (4) compatibility.  Independence is the unexamined status quo, compatibility a pipe dream, and conflict is right out.  I love, love, love dialogue.

 

The relationship I have demonstrated above is (2) a dialogue between the worldview of science and the worldview of art.  One might subclassify it as (2a) science helps art.  Ms. Galloway asked me to help her.  I did everything I could to do so.

 

Science and art are not incompatible, here obviously.  But mark me well.  Science and art are not compatible either.  They are very simply, and very profoundly, different.  Ms. Galloway is an artist, and she took the lead in this interaction, and I (a scientist) did what I could to help her create a work of art, and at no point did anything that happened between us during our entire two-week interaction have anything to do with science whatsoever.  The pleurocerid images she carved into that pot could bear sinistral shells, or dextral shells, or polka-dot shells, it does not matter.  And in fact, she never asked me for any of the free advice I offered her at any point, and in retrospect, I may have been interfering with the creative process, and if I ever hear from her again, I will apologize for butting in.

 

But I can’t help it, I love that sort of thing. The proper relationship between our worldviews is one of dialogue.  A dialogue with a fine artist is like an expedition into the bush with a Hottentot, from the seat of my own kitchen table.

 

And here is the most interesting thing about my two-week dialogue with Ms. Galloway.  This particular artist’s motivation was not artistic, but political. 

 

The Oxford Dictionary defines art as “an expression of human skill producing works to be appreciated primarily for their beauty or emotional power.”  But to quote from Ms. Galloway’s website, she considers her work “a catalyst for social change.” 

 

She selected Anthony’s Riversnail as one of her 1,200 subjects because that particular gastropod was entered onto the Federal Endangered Species list on April 15, 1994, see 59 FR 17994-17998 [5]. And “By creating an urn for each (such) species, (she) is making (rarely-seen) species visible, and through this awareness, compassionate action is possible.”  In other words, Ms. Galloway apparently thinks that the worldview of art and the worldview of politics are compatible, such that the former can influence the latter.

 

Bless her heart.  You will have by now noticed that no representative from the world of politics or public policy walked into the bar with the artist and the scientist to this point in my essay, nor will one subsequently appear.  I myself was awarded a AAAS Congressional fellowship many years ago, and learned just enough of the language spoken on Capitol Hill 1981 – 82 to appreciate my limitations.  And I do know quite a few hardworking biologists employed by natural resource agencies, both state and federal. And speaking now for all the legislative bodies and all the regulatory agencies and all the departments of natural resource management involved in all the endangered species conservation nationwide, as well as the entire [6] gastropod fauna of Limestone Creek, Madison County, Alabama, thanks for the pot.  Not a great likeness, but it’s lovely, dear, it really is.

Dave Michaelson & Randy Sarver

Art and Public Policy have different languages, different cultures, different values, and different ways of looking at the world. That they are not incompatible is witnessed by Ms. Galloway herself, who is both an artist and a social activist.  But the worldviews are not compatible, either.  Neither art nor public policy can affect the other, any more than the marching band affects the halftime score, or the halftime score the marching band.

 

But lest we condescend.  Of all the holders of all the worldviews of all the world – Art, Science, Business, Finance, Law, Medicine, Engineering, Religious Faith, Harry Potter, or Star Trek, we scientists are the most arrogant.  The notion of science-based public policy is just as absurd as pottery-based public policy, and none of us seems to realize it.

 

On the morning of 4Sept25, the same day I was to send my fourth email to Ms. Galloway, I met my good friend Randy Sarver in the parking lot of the Missouri Department of Natural Resources, Jefferson City. Randy is an excellent biologist, and we have developed a warm relationship over many years, and he helped me unload four flats of empty black-capped vials that used to hold macrobenthic samples collected by the MoDNR 2015 - 2017, and swap them for a fresh batch of MoDNR macrobenthic samples 2017 - 2018. 

 

I am sure that Randy and Dave Michaelson and all our friends at the MoDNR do a great job monitoring the water quality of the Show-Me State, and I would never dream of offering them any advice whatsoever, because I can’t, any more than they would dream of offering me any advice about malacology, because they can’t.  Randy and I are in dialogue.  That’s the thing I love.

 

Notes:

 

[1] I actually did post one previous essay on the relationship between science and art, way back in 2011:

• When Science and Art Collide [4Feb11]

 [2] Learn more about Ms. Galloway from her lavish web presence:

• Julia Galloway [home]
• Endangered Species Project [direct]
• Wikipedia [page]

 [3] Wikipedia, accessed 10Dec25 [link]

 

[4] Here I am generalizing Barbour’s thought on the science – religion relationship to the relationship between worldviews of any sort.  His “fourfold typology” was most clearly stated in:

• Barbour, I. G. (2000) When Science Meets Religion: Enemies, Strangers, or Partners?  Harper, 205 pp.

[5] For the Democrats among my readership, who imagine that findings such as those published in the Federal Register on 15Apr94 have anything to do with science whatsoever, please refresh your memory with the ten essays I have written on the Snake River Physa scandal to date.  Actually, you could skip the first six, if you want, and go straight to:

• The SRALP and the SRNLP: A new hope [14May24]
• The SRALP and the SRNLP: Physa acuta were found [11June24]
• The Twelve Phascinating Physa of Bliss [2July24]
• Cytoplasmic Male Sterility in the Snake River Physa [7Aug24]

[6] Fourteen species comprise the exuberant gastropod fauna of Limestone Creek: four pleurocerids, three hydrobioids [7], three viviparids, and four pulmonates.  I feel certain that all have benefited from the endangered status of their most-famous member.

[7] Counted among the Limestone Creek hydrobioids is a population of Marstonia olivacea, which is a senior synonym of Marstonia ogmorhaphe, which was the other gastropod entered onto the Federal Endangered Species list 15Apr94.  And hence that hydrobiid population should be every bit as federally-protected as the pleurocerid "Athearnia anthonyi," but it isn't, because public policy has absolutely nothing to do with science.  For more, see:

• Is Marstonia olivacea extinct? [19Sept23]

Anchored hybrid enrichment, Leptoxis lessons, and the advice of Queen Elsa

Editor’s Note – This is the third installment of a three-part series reviewing the 2022 paper by Whelan and colleagues [1] on “Prodigious polyphyly in the Pleuroceridae.”  We recommend that you back up and read both our posts of September [23Sept25] and October [14Oct25] if that material isn’t fresh in your mind.  You will also find our posts of [6Apr23] and [9May23] helpful as background for the essay that follows, if you want to dig more deeply into the subject matter itself.

Back in early September I enjoyed a wonderful two-week field trip to the Ozark/Ouachita Highlands of Arkansas, southern Missouri, and eastern Oklahoma, logging 3,700 miles on my pickup and 20 miles on my kayak, collecting 59 sites.  And I am looking forward to sharing a lot of stories about my adventures in that biogeographically fascinating part of the world with you all in future posts.  Some of the observations I made on Leptoxis arkansensis during that memorable excursion are, however, especially relevant to the “prodigious polyphyly” discovered by Nathan Whelan and his colleagues [1] in the AHE phylogenomic study we are currently reviewing.

Populations of Leptoxis arkansensis are uncommon and widely scattered in the region, primarily inhabiting the rocky riffles of small rivers with good water quality, always (as far as I can tell) co-occurring with large and nearly-omnipresent populations of Pleurocera potosiensis.  From all evidence, the two are distinct biological species.  The shells borne by L. arkansensis demonstrate a larger body whorl than those of P. potosiensis, consistently and reliably, from birth to maturity.  But their grossly similar morphology in overall shell form can render the two species difficult to distinguish in the field.  There is not a shadow of doubt in my mind that they are “sister” species, one evolved from the other.

The strongest hypothesis, I would suggest, is that the original population of Leptoxis arkansensis evolved from a Pleurocera potosiensis population specialized for life in the riffles at midstream, and that the larger body whorl reflects a relatively larger foot, adapted for clinging to rocks in rapid currents.  Might that same adaptation have evolved more than once in the hundred-million-year history of the North American Pleuroceridae?  Who among my vast and erudite readership could imagine any answer to my rhetorical question other than the affirmative [2]?

The most loyal and patient among you might remember a (rather personal) essay I posted back in [6Apr23] entitled, “Growing Up With Periwinkles.”  In that post I reviewed my own 60+ years of experience with Leptoxis in the Southern Appalachians, from childhood through college and into my professional career, including several allozyme studies and even one (rather atypical, for me) sequence study as well.  I concluded that essay as follows: “If you had asked me ten years ago, I would have listed six valid species of Leptoxis in North America: carinata, praerosa, crassa, picta, plicata, and maybe that weirdo way out in the Ozarks, Leptoxis arkansensis (Hinkley 1915), I have no reason to doubt.”

Then, in the essay that followed [9May23], I “tested the periwinkle hypothesis” with the four-gene phylogeny (CO1, 16S, 28S, H3) that Nathan Whelan developed for his (2013) dissertation [3], finding solid agreement with my six-species model.  The main trunk of Nathan’s gene tree showed L. praerosa, L. crassa, L. carinata and L. picta distinct as expected.  Leptoxis plicata and L. arkansensis were also distinct, but depicted way off in the distant foliage with a variety of pleurocerids representing other genera.

There was also one surprise – evidence of a cryptic species sympatric with Leptoxis praerosa through much of their shared range in East Tennessee and North Alabama.  Nathan identified that cryptic species, quite problematically, as Leptoxis virgata. At the end of my [9May23] essay I had renamed my hypothesis for the genus Leptoxis in North America the 6* Species Model, adding that asterisk for the possibility of a seventh, cryptic species.

Figure 4 of Whelan et al [1]

Both of those 2023 essays were focused entirely on evolutionary relationships at the species level and below.  I wouldn’t say that I myself am entirely disinterested in evolution at higher levels, it just seems to me that we ought to work out some plausible hypotheses for the populations and the species first.  So now, with the 6* Species Model firmly supported both by Nathan’s 4-gene dissertation and by my own 60+ years of experience in field and laboratory, we are in a position to understand what Nathan’s more recent AHE phylogenomic analysis is telling us about the evolution of Leptoxis as a genus.  Then starting at three o’clock in Nathan's circular-format AHE tree above, and proceeding clockwise:

Leptoxis picta.  Way back in 1998, our good buddy Chuck Lydeard and I published a paper [4] showing that the allozyme divergence among six populations of three nominal species of Alabama Leptoxis: L. picta, L. ampla, and L. taeniata (subsequently [5] renamed coosaensis), was no greater than the divergence among control Leptoxis populations sampled from the Tennessee drainage, which nobody had ever suggested were anything other than L. praerosa.  We suggested that those three Mobile Basin nomina be united under the oldest name, Leptoxis picta (Conrad 1834).

Since 1998, an impressive body of research has been published supporting that hypothesis.  Nathan’s four-gene dissertation [3] returned negligible divergence among picta, ampla, taeniata/coosaensis, and foremani (7 populations, 18 individuals).  And both of Nathan’s (really quite lovely) subsequent studies of interpopulation divergence in “Leptoxis ampla,” his (2016) study of mitochondrial superheterogeneity [6] and his (2019) RADseq study [7], recovered strikingly high levels of interpopulation divergence, which easily extrapolate to include Mobile Basin populations historically identified as picta, taeniata/coosaensis, and foremani.

Now open before us we have a fifth study, estimating levels of genetic divergence among 192 individual pleurocerid snails over their entire single-copy genomes using the cutting-edge technique of Anchored Hybrid Enrichment, showing exactly the same result as references [3], [4], [6], and [7].  The nomina ampla, coosaensis, foremani and taeniata are all obsolete, junior synonyms of L. picta.  And to find the branches of a 21st century phylogenomic tree cavalierly decorated all about its entire periphery with 19th century superstition is an embarrassment to our entire profession.

Leptoxis carinata.  Quite independently of the evolution of Leptoxis picta in the Mobile Basin of Alabama, Nathan’s AHE phylogenomic analysis suggests a second origin of the genus Leptoxis in the southern Appalachians.  This origin is likely much older.

The sequencing studies I published with John Robinson in 2009 confirmed that Ohio drainage populations identified as Leptoxis dilatata (Conrad 1835) are conspecific with Atlantic drainage populations identified (since 1792!) as Leptoxis carinata, and suggested that the pleurocerid fauna of this ancient region might have evolved at the (Paleozoic) Appalachian orogeny [8].  Both the conspecific status of the two nomina, and the origin of Leptoxis carinata (now more broadly and properly understood) independent of any other Leptoxis species, were confirmed by Nathan’s dissertation [3], and have now been triple-checked by the AHE phylogenomic analysis under review here.

Leptoxis crassa and praerosa.  Again dovetailing nicely with his (2013) dissertation research, Nathan’s big AHE phylogenomic analysis confirms that Leptoxis crassa (identified here under the obsolete [9] synonym “Athearnia anthonyi”) is related to, but specifically distinct from, Leptoxis praerosa.  And the larger set of crassa + praerosa together apparently represents a third independent evolution of the shell morphology we associate today with the genus Leptoxis.  This third origin seems to have occurred in the Tennessee/Cumberland region, I should guess after Leptoxis carinata evolved further east, but before L. picta to the south.

Burrowing more deeply into that lovely lavender subcluster, we find further confirmation of Nathan’s 2013 results suggesting that umbilicata (Weatherby 1876) and subglobosa (Say 1825) are junior synonyms of L. praerosa (Say 1821).  Somewhat surprisingly, however, Nathan’s AHE analysis did not return evidence of any significant genetic distinction between two individuals he identified as L. virgata (only one of which is depicted below) and the larger L. praerosa cluster.

You might recall from my [9May23] review of Nathan’s dissertation that he did not specify any morphological trait by which his L. virgata could be distinguished from sympatric populations of L. praerosa, and that the genetic difference was apparently only mitochondrial, not nuclear.  Here ten years later, we are left wondering whether Nathan might have misidentified both of his nominal virgata specimens in 2022, or if the evidence he adduced in 2013 that a second biological species might be cryptic under our old friend Leptoxis praerosa might have been an atypically widespread case of mitochondrial superheterogeneity [11].

 

Leptoxis arkansensis.  We reviewed this branch of Nathan's AHE phylogenomic tree at the top of this essay.  The independent origin of Leptoxis arkansensis way out west in the Ozark highlands seems to be yet a fourth evolution of the shell morphology we associate today with the genus Leptoxis. 

 

Leptoxis plicata.  Even as the 1998 allozyme study of Dillon & Lydeard [4] was returning conspecific levels of genetic divergence among Alabama populations of Leptoxis picta, ampla, and taeniata/coosaensis, a fourth nominal species of Leptoxis from the state of Alabama, Leptoxis plicata, was revealed to be genetically distinct.  The single population of L. plicata known at that time, inhabiting the Locust Fork of the Black Warrior River, bore shells with a characteristically high apex and weak but distinctive plication on the upper whorls. 

 

From Whelan et al [1]

Additional evidence for the validity of L. plicata as a biological species was brought to light in 2013, with the publication of Nathan Whelan’s dissertation [3]. Nathan’s four-gene phylogeny depicted L. plicata as quite distantly removed from the other Alabama Leptoxis species, distant indeed from (almost) all other populations ever identified as Leptoxis anywhere, way off on a branch with clusters of Pleurocera and Lithasia.

Regarding that parenthetical modifier, “almost.”  I did not mention it at the time of my [9May23] review, but it is certainly worthy of note today, that in 2013 Nathan seems to have found very little sequence divergence between Leptoxis plicata and a newly-rediscovered Leptoxis population inhabiting the Cahaba River about 50 km south of Locust Fork, which he identified as Leptoxis compacta [13].  Here’s the copy of Nathan’s gigantic Baysian tree that I first made available for download from my 2023 review, with the little plicata/compacta cluster encircled in red:

[Whelan 2013 Figure 5.4, modified]

To objectively evaluate the significance of the evolutionary relationship between L. plicata and L. compacta, perhaps among the first data sets of interest would be their percent sequence divergence.  Alas, Nathan never uploaded any of the sequence data from his massive dissertation to GenBank.  But holding Nathan’s gigantic 2013 gene tree at arm’s length and scanning for an overall impression, L. plicata and L. compacta appear conspecific, the former nomen (Conrad 1834) having priority over the latter (Anthony 1854).

Now here ten years later, we find Leptoxis plicata and L. compacta again depicted as conspecific in Nathan’s AHE phylogenomic tree.  I myself have no biological insight to contribute, my experience with the legendary pleurocerid fauna of the Cahaba River being limited to song, story, and musty chronicle.  The descriptions I have read and the figures I have seen of the L. compacta shell do not mention shell plication, but do show the same unusually high spire characteristic of L. plicata.

In any case, I am sure we can all agree that the shell morphology borne by the Locust Fork / Cahaba pleurocerid populations together, clustered as both are upon the far-flung branches of every gene tree they’ve ever hung, suggests yet another separate origin of the genus Leptoxis.

 

So, to summarize the first 71% of the present essay.  Nathan’s AHE phylogenomic analysis confirms the 6-Species Model for the genus Leptoxis, without an asterisk.  The rocky shoals of North American rivers are inhabited by, in order of their description, Leptoxis carinata (Brug. 1792), L. praerosa (Say 1821), L. picta (Conrad 1834), L. plicata (Conrad 1834), L. crassa (Hald. 1841), and L. arkansensis (Hinkley 1915).  And the shell morphology that has historically served to unite these six biological species into the genus Leptoxis has evolved five separate times.

 

The first genus-level name to be proposed for the freshwater cerithiaceans of North America was, apparently [14], Pleurocera. And it was the eccentric French naturalist Constantine Rafinesque who did the proposing, way back in 1818.  The shell that he seems to have had in his hand at that time was elongate, with a high spire and small body whorl, best-guess-identified today as Pleurocera canaliculata [15].

 

And the second genus-level name proposed for the North American freshwater cerithiaceans was like unto the first, also proposed by Rafinesque, one year later.  That genus name was Leptoxis.  And the shell that Rafinesque seems to have had in his hand at that juncture was rotund and obovate, with a low spire and a large body whorl, best-guess-identified today as Leptoxis praerosa [15].

 

Thus, it seems that even prior to the birth of American malacology, when Frenchmen were still running around loose in our backwoods with butterfly nets, everybody who has ever pulled more than one pleurocerid snail out of our crystal-clear waters has divided out a subset bearing shells that are elongate and a subset bearing shells that are obovate.

Rafinesque (1783-1840)

Additional subsets were carved out as the nominal species accumulated, of course.  Generally following Goodrich, Burch [10], suggested a seven-genus system for the North American Pleuroceridae, most of those seven genera with subgenera, and listed an additional 25 genus names in synonymy.  But that elongate/obovate dichotomy has always been the most fundamental, and the Pleurocera/Leptoxis division the first.

So today we sit at our desks, a remarkably plausible reconstruction of the evolutionary history of the North American Pleuroceridae blossoming before us in lovely pastel shades of yellow, green, blue, and lavender.  And it seems quite appallingly evident that the very first taxonomic distinction made by our forefathers, around which 200 years of taxonomy subsequently developed, has no evolutionary basis.  Shall we then discard the entire richly historic but scientifically obsolete classification system of the Pleuroceridae?

 

No.  The binomial system of nomenclature was not first proposed by Carl Linnaeus in 1758 for any evolutionary purpose whatsoever.  It was first a tool for information storage and retrieval, and it served that function alone for its first 100 years of application, carrying Darwin toward the Theory of Evolution just as surely as The Beagle.  And that information-retrieval function continues to be the primary utility of biological taxonomy even to the present day.

 

I absolutely understand that the names of organisms must be changed to reflect scientific advance, and have certainly done my fair share of the changing.  But when we change a name, we pay the price of losing some of the information that the previous name historically transmitted.

 

The reason I synonymized Goniobasis and Elimia under Pleurocera in 2011 [16] was my discovery that single randomly-breeding populations of freshwater gastropods were being classified into three genera – not just in one case, but repeatedly, throughout the North American pleurocerid fauna.  The cost of the misinformation being generated by the Pleurocera/Goniobasis/Elimia confusion outweighed, in my judgment, the cost of the good information lost by the combination of those three names.

 

And I would invite Nathan Whelan and all our mutual colleagues, once again, to follow suit on that.  Look at that tangle of blue and yellow branches in the GHIJKL quadrant of your tree, colleagues!  Your own analysis shows that there is no evolutionary basis for the genus name “Elimia.” 

 

I understand your fervent desire to preserve obsolete nomina for the information they transmit.  I would point out, however, that “Goniobasis” contained even more information than “Elimia” when Burch [10] high-handedly dumped Goniobasis for an obscure point of taxonomic priority in 1980, yet our discipline survived.  And I would argue that the profits we all stand to gain by correcting the misinformation being promulgated even unto the present day by the entirely artificial distinction [17, 18] between Elimia and Pleurocera far outweigh the loss of good information we will suffer synonymizing the former under the latter.

 

But as to the other Burch/Goodrich genera – Lithasia, Io, Gyrotoma and especially Leptoxis, I believe that we have now reached consensus.  Can we all agree to take Queen Elsa’s advice, henceforth?  Let it go.

Notes:

 

[1] Whelan, N. V., Johnson, P. D., Garner, J. T., Garrison, N. L., & Strong, E. E. (2022). Prodigious polyphyly in Pleuroceridae (Gastropoda: Cerithioidea). Bulletin of the Society of Systematic Biologists, 1(2). https://doi.org/10.18061/bssb.v1i2.8419

 

[2] Here I have answered a rhetorical question with a second rhetorical question.  And this isn’t even rhetoric, it is prose.  Have I violated some ancient and hoary guideline?  If so, I plead ignorance, and apologize.

 

[3] Whelan, Nathan V. (2013) Conservation, life history and systematics of Leptoxis Rafinesque 1819 (Gastropoda: Cerithioidea: Pleuroceridae).  PhD Dissertation, University of Alabama, Tuscaloosa.  179 pp.  For a review, see:

• Testing the periwinkle hypothesis [9May23]

[4] Dillon, R.T., and C. Lydeard (1998) Divergence among Mobile Basin populations of the pleurocerid snail genus, Leptoxis, estimated by allozyme electrophoresis.  Malacologia. 39: 111-119. [pdf]

 

[5] Whelan, Nathan V.; Johnson, Paul D.; Garner, Jeffrey T.; Strong, Ellen E. (2017). On the identity of Leptoxis taeniata – a misapplied name for the threatened Painted Rocksnail (Cerithioidea, Pleuroceridae). ZooKeys (697): 21–36. https://zookeys.pensoft.net/article/14060/

 

[6] Whelan, N.V. & E. E. Strong (2016) Morphology, molecules and taxonomy: extreme incongruence in pleurocerids (Gastropoda, Cerithiodea, Pleuroceridae). Zoologica Scripta 45: 62 – 87.  For a review, see:

• Mitochondrial superheterogeneity and speciation [3May16]

[7] Whelan, N.V., M.P. Galaska, B.N. Sipley, J.M. Weber, P.D. Johnson, K.M. Halanych, and B.S. Helms (2019)  Riverscape genetic variation, migration patterns, and morphological variation of the threatened Round Rocksnail, Leptoxis ampla.  Molecular Ecology 28: 1593 – 1610.  For a review, see:

• Intrapopulation gene flow, the Leptoxis of the Cahaba, and the striking of matches [2Nov21]

[8] Dillon, R T. and J. D. Robinson (2009) The snails the dinosaurs saw: Are the pleurocerid populations of the Older Appalachians a relict of the Paleozoic Era?  Journal of the North American Benthological Society 28: 1 - 11. [pdf] For a review, see:

• The snails the dinosaurs saw [16Mar09] 

[9] Jack Burch [10] lowered “Athearnia” to subgeneric status under Leptoxis way back in 1980, as he lowered “anthonyi” to subspecific status under crassa.  The relentlessly archaic taxonomy to which Nathan Whelan and his colleagues cling is not even current to the 20th century, much less the 21st.

 

[10] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI).

 

[11] The phenomenon of mitochondrial superheterogeneity was first documented in the pleurocerid snails by Dillon & Frankis [12] and made famous in 2009 by Dillon & Robinson [8].  The term was not actually coined until 2016, however, in a series of posts on this blog.  See:

• Mitochondrial superheterogeneity: What we know [15Mar16]
• Mitochondrial superheterogeneity: What it means [6Apr16]
• Mitochondrial superheterogeneity and speciation [3May16] 

[12] Dillon, R. T., and R. C. Frankis. (2004) High levels of DNA sequence divergence in isolated populations of the freshwater snail, Goniobasis.  American Malacological Bulletin 19: 69 - 77 [pdf].

 

[13] Whelan NV, Johnson PD, Harris PM (2012) Rediscovery of Leptoxis compacta (Anthony, 1854) (Gastropoda: Cerithioidea: Pleuroceridae). PLoS ONE 7(8): e42499. https://doi.org/10.1371/journal.pone.0042499

 

[14] The actual meaning of Rafinesque’s 1818 nomen “Pleurocera” was shrouded in mystery and roiled by controversy for many years.  For a review, see:

• Joe Morrison and the great Pleurocera controversy [10Nov10] 

[15] Both Pleurocera canaliculata and Leptoxis praerosa were described by Thomas Say in 1821.  Yes, it is possible to describe a genus before its type species.

 

[16] Dillon, R. T. (2011) Robust shell phenotype is a local response to stream size in the genus Pleurocera (Rafinesque 1818). Malacologia 53: 265-277 [pdf]. For a review, see:

• Goodbye Goniobasis, Farewell Elimia [23Mar11] 

[17] For a demonstration of the artificiality of the genus nomen Elimia, see:

• Goniobasis and Elimia [28Sept04] 

[18] And for a demonstration of the artificiality of the genus nomen Goniobasis, see:

• A House Divided [10May20]